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Esthetic orthodontic treatment with a double J retractor and temporary anchorage devices
CLINICIAN'S CORNER
Esthetic orthodontic treatment with a double J retractor and temporary anchorage devices Jae Hyun Park,a Kiyoshi Tai,b Masato Takagi,c Kuniaki Miyajima,d Yukio Kojima,e and Bo-Hoon Joof Mesa, Ariz, Okayama and Nagoya, Japan, St Louis, Mo, and Seoul, Korea
This clinical article reports an esthetic treatment option for managing a Class II malocclusion in an adult. The patient, a woman aged 24 years 2 months, had crowding and a convex profile. She was treated with maxillary first premolar extractions, a double J retractor, and temporary skeletal anchorage devices in the maxillary arch. Posttreatment records after 2 years showed excellent results with good occlusion and long-term stability. (Am J Orthod Dentofacial Orthop 2012;141:796-805)
T
he correction of dental crowding is a common orthodontic treatment that can be performed with a removable or fixed appliance or a combination of both. Until recently, the process of straightening teeth has typically involved appliances including brackets, bands, and wires, but many adult patients are reluctant to wear fixed appliances. Consequently, the desire for a cosmetic solution for misaligned teeth has caused more patients to seek veneers, crowns, and other laboratory-fabricated cosmetic restorations. Clear brackets can be placed for esthetic reasons, but they can irritate soft tissues because of their size. Lingual brackets might be a great alternative for those who desire straight teeth without visible brackets, but, although lingual orthodontic techniques have improved, they generally require more chair time and might not be cost-effective.1,2 Clear removable appliances have the benefits of improved oral hygiene and esthetics.3-6
a Associate professor and chair, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, Mesa, Ariz; international scholar, Graduate School of Dentistry, Kyung Hee University, Seoul, Korea. b Visiting adjunct assistant professor, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, Mesa, Ariz; private practice, Okayama, Japan. c Private practice, Okayama, Japan. d Adjunct professor, Center for Advanced Dental Education, Saint Louis University, St Louis, Mo. e Associate professor, Department of Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan. f Adjunct professor, Department of Orthodontics, Samsung Medical Center, College of Medicine, Sungkyunkwan University, Seoul, Korea; private practice, Seoul, Korea. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Jae Hyun Park, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, 5835 E Still Cir, Mesa, AZ 85206; e-mail, [email protected]. Submitted, August 2010; revised and accepted, January 2011. 0889-5406/$36.00 Copyright Ó 2012 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2011.01.024
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These appliances have become increasingly popular among adults who want to straighten their teeth without using conventional brackets. However, in orthodontics, precisely controlled force application is required to achieve the final alignment. The purpose of this article is to report the use of a modified type of lingual retractor, the double J retractor, and temporary skeletal anchorage devices for enmasse retraction of the 6 anterior teeth in a patient with premolar extractions.7
DIAGNOSIS AND ETIOLOGY
A woman aged 24 years 2 months was referred by a general dentist for evaluation of anterior crowding. Her chief complaint was the appearance of her maxillary anterior teeth and upper lip (Fig 1). She did not want to have fixed orthodontic appliances in the maxillary arch because of their appearance, especially when smiling. She had a convex profile and a Class II skeletal pattern, with a Class II Division 1 malocclusion. Her facial form was mesocephalic, with good symmetry, a mildly increased lower facial height, and a retrognathic chin. Lip competence could be achieved but with some mentalis strain. There were no signs of temporomandibular joint dysfunction, and mandibular movements were normal, with no evidence of deviation. Intraorally, her maxillary and mandibular midlines were centered relative to her facial midline. All permanent teeth were present, and she had fair oral hygiene and probing depths within the norms. The patient was in good general health and had no history of major systemic diseases. She had no history of dental trauma or parafunctional habits, and the etiology of her occlusion was believed to be heredity. Pretreatment records showed that the patient had an end-on Class II relationship on the right and the left at the
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Fig 1. Pretreatment facial and intraoral photographs.
first molars and canines. There was moderate crowding in the maxillary arch and mild crowding in the mandibular arch with a severe curve of Spee. She had a 6.3-mm overjet and an 80% overbite. The teeth were free of caries with no pathologies. The third molars were missing. The cephalometric analysis indicated skeletal Class II (ANB, 8.4 ; Wits, 3.6 mm) with a hyperdivergent growth pattern (SN-MP, 44.9 ). The maxillary incisors were slightly retroclined (U1-SN, 96.2 ) caused by bilateral rotation of the maxillary central incisors, and the mandibular incisors showed a slight retroclincation (IMPA, 88.3 ) (Fig 2; Table). TREATMENT OBJECTIVES AND PLAN
The treatment objectives were to obtain normal overjet and overbite, establish Class I canine and molar relationships, relieve the crowding in both arches, level the
curve of Spee, and improve the patient's profile without the use of labial fixed appliances in the maxillary arch. With temporary skeletal anchorage devices, distal movement of the anterior or posterior teeth or both, without anchorage loss, would be possible.8,9 This patient wanted to retract her upper lip as much as possible, so the maxillary first premolars were extracted, but, to camouflage the skeletal Class II pattern, the mandibular second premolars were not extracted. TREATMENT ALTERNATIVES
With no growth modification possible, correction of the Class II molar relationship could be accomplished by nonextraction molar distalization treatment, extraction of the maxillary first premolars and the mandibular second premolars, or extraction of only the maxillary first premolars.
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Fig 2. Pretreatment panoramic radiograph and lateral cephalogram.
Table. Cephalometric measurements Measurement SNA ( ) SNB ( ) ANB ( ) Wits (mm) SN-MP ( ) FH-MP ( ) LFH (ANS-Me/N-Me) (%) U1-SN ( ) U1-NA ( ) IMPA ( ) L1-NB ( ) U1/L1 ( ) Upper lip (mm) Lower lip (mm)
Japanese norm 82.0 80.0 2.0 1.1 32.0 25.0 55.0 104.0 22.0 90.0 25.0 124.0 1.2 2.0
Pretreatment 83.5 75.0 8.4 3.6 44.9 35.0 57.1 96.2 12.8 88.3 28.2 130.6 4.1 4.8
To accomplish the treatment objectives, conventional esthetic treatment options for the maxillary orthodontic appliances included lingual orthodontic appliances or clear removable appliances. However, a difficult problem to overcome in lingual orthodontics has been torque control of the anterior teeth. A potential disadvantage of clear removable appliances is that they highly depend on patient compliance.6 The other significant weakness is the aligner cannot move the root apex efficiently which results in the tipping of teeth especially in extraction cases. Compared with those 2 esthetic orthodontic appliances, the double J retractor offered an effective tool for producing translational tooth movement during anterior retraction; a treatment plan was developed that included extraction of the maxillary first premolars, delivery of the double J retractor, and use of temporary skeletal anchorage devices to achieve bodily translation. Because of the skeletal discrepancies that resulted from an unfavorable growth pattern, bilateral sagittal
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Posttreatment 82.1 74.9 7.2 4.7 45.2 35.9 57.4 90.7 8.5 91.7 31.0 133.2 0.8 2.2
2 years posttreatment 79.9 75.1 4.8 2.7 45.0 35.3 57.3 94.7 14.8 88.3 28.7 131.7 0.6 2.0
split osteotomy was discussed for mandibular advancement combined with orthodontic treatment. Upon completion of the orthodontic treatment, genioplasty would be another option to improve her profile, but the patient declined all surgical options. TREATMENT PROGRESS
Before orthodontic treatment, the patient was referred to an oral surgeon to extract her maxillary first premolars. Because she had high esthetic demands and was unwilling to tolerate the extraction spaces, esthetic pontics were bonded to the distal aspects of the maxillary canines. The double J retractor is an alternative method for obtaining the desired direction of force on the maxillary anterior teeth.10-12 We used bonding pads instead of mesh brackets, which were common with earlier lingual retractors. The anterior lever arm hooks were bent in the wire approximately 20 mm from the pad so
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Fig 3. A, Schematic showing the double J retractor and palatal temporary anchorage devices: 1 and 2, palatal temporary skeletal anchorage devices; 3, anterior lever arm hooks; 4, posterior lever arm hooks. B, Maxillary occlusal photograph during treatment with a double J retractor and temporary skeletal anchorage devices. C, Maxillary occlusal photograph showing the bonded fixed appliance.
that the line of action of the force passed through the center of resistance. The posterior lever arm hooks were extended from the lingual crown surfaces of the canines. Both hooks can be used for space closing with elastic chains or superelastic closed-coil springs, and the posterior hooks can be used for torque control with Class II elastics. In this case, however, to minimize extrusion of the posterior mandibular teeth, the patient wore the Class II elastics at night only when it was necessary. After the retractor was adjusted to the lingual surface of the anterior teeth, it was bonded to them. Transbond (3M Unitek, Monrovia, Calif) was used, in addition to the customary bonding adhesive, to resist the shearing forces that occur when loading the retractor.13 Three temporary skeletal anchorage devices were placed (OSAS, Tuttlingen, Germany). Two (diameter, 1.6 mm; length, 8.0 mm) were placed palatally between the maxillary first and second molars, and 1 temporary anchorage device (diameter, 1.6 mm; length, 7.0 mm) was placed in the midpalate. Elastic chains or superelastic closed-coil springs were stretched from the anterior hooks to the temporary skeletal anchorage devices (Fig 3). A cephalometric film was used to determine the point of force application of the appliance with the aid of a gutta-percha cone as a radiopaque guide. Power elastic chains or nickel-titanium closed-coil springs that delivered 200 g per side provided the retraction force for space closure.14 In addition, the intrusion force of the lingual retractor was 60 g per side.15 Biomechanically, the position of the hook in the lever arm wire can change the point of force application with respect to the center of resistance of the teeth to be intruded and retracted. During lingual retraction, the maxillary left posterior temporary skeletal anchorage device failed, so another (diameter, 1.6 mm; length, 8.0 mm; OSAS) was installed between the maxillary left second premolar and first molar. After 6 months, the anterior teeth were retracted so that only 1 to 1.5 mm of space
remained between the canines and the second premolars. At this point, the patient was satisfied with the results, and she agreed to allow the fixed appliances be bonded for axial control and root movement. The 0.022 3 0.028-in edgewise ceramic brackets were bonded in both arches. After leveling, 0.018 3 0.025in stainless steel wires were placed for the remaining space closure in the maxillary arch. At this point, the patient wanted to retract her upper lip a bit more. Because of her request during the space closure, the maxillary anterior teeth were slightly tipped lingually (Fig 3). In the mandibular arch, during the leveling stage, a sectional 0.016-in copper-nickel-titanium wire was used between the mandibular incisors to achieve their initial leveling. Then a mandibular utility archwire was constructed with 0.016 3 0.022-in stainless steel wire. With a mandibular utility archwire, intrusive forces were applied to the mandibular incisors labially to the center of resistance. It produced a labial crown moment that resulted in proclination of the mandibular incisors.16 To minimize this side effect, labial root torque was included in the incisor region of the mandibular utility archwire.17,18 To produce approximately 60 g of incisor intrusion force, 20 of distal molar crown tip was activated.18 To prevent the need for mandibular molar extrusion, buccal root torque and expansion were applied to the molars by establishing cortical anchorage.18 After leveling the mandibular arch, a flat 0.016 3 0.022-in nickel-titanium archwire was used. At the finishing stage, a mild curve of Spee in the maxillary archwire and a mild reverse curve of Spee in the mandibular archwire were placed by using 0.018 3 0.025-in stainless steel wires. To establish acceptable overbite and overjet, intreproximal reduction was done on the mandibular anterior dentition during the finishing stage. A tooth positioner was used for final detailing. After treatment, the curve of Spee of the mandibular arch was found to be
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Fig 4. Three-dimensional finite element model for tooth-periodontal ligament system.
Fig 5. Retraction forces with A and B, temporary skeletal anchorage devices and C, elastics produce rotation of the anterior segment around the center of resistance.
successfully leveled. Active treatment time was 18 months. For a better esthetic result, an advancement genioplasty could have been considered. After treatment, maxillary and mandibular Essix retainers (Dentsply Raintree Essix, Sarasota, Fla) were delivered. The patient was instructed to wear them 24 hours per day for 1 year and then at night only. Recall visits for retainer checks occurred at 1, 3, and 6 months during the first year. To ensure continued satisfactory posttreatment alignment of the mandibular and maxillary anterior dentition, the use of retainers was recommended indefinitely.19 The detailed calculation method has already been described in previous articles.20,21 For our patient, the double J retractor was constructed of a segmented archwire bonded to the 6
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anterior teeth, and lever arms extended from the segmented archwire. Both were made of a stiff 0.028-in steel wire (Young's modulus, 200 GPa), and forces were applied at the ends of the lever arm. Assuming symmetry on both sides of the arch, a model of only the left side was fabricated. A lateral view of the finite element model is shown in Figure 4. By using this method, orthodontic tooth movement is calculated based on bone remodeling: ie, resorption and apposition of the alveolar bone. The boneremodeling rate is assumed to be in proportion to stress in the periodontal ligament. Jang et al7 reported that the center of resistance of the 6 maxillary anterior teeth is located vertically 12.2 mm (55.6%) and apically to the incisal edges of central incisors. Those authors also demonstrated that
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Fig 6. Posttreatment facial and intraoral photographs.
temporary skeletal anchorage devices located 8 mm apically to the cervical line of the first molars achieved bodily anterior retraction with a double J retractor. The center of resistance of the anterior teeth was determined from movement patterns when changing the location of the lever arm end. Figure 4 shows the movement patterns of the 6 anterior teeth and the stress distributions in the periodontal ligament after retraction of the teeth by 4 mm. When an extension line of the force passed through the center of resistance of the 6 anterior teeth, the teeth moved bodily and intruded by 0.5 mm. When an extension line of the force was coronal to the center of resistance, the anterior teeth tipped lingually. When an extension line of the force was apical to the center of resistance, there was lingual root movement (Fig 5). TREATMENT RESULTS
The posttreatment records demonstrate that the treatment objectives were achieved. The facial
photographs showed improved smile and profile esthetics (Fig 6). Class I canine and Class II molar relationships were established with a canine-protected occlusion. The dental midlines were maintained with the facial midline, and ideal overbite and overjet were achieved, and the curve of Spee was successfully leveled. The posttreatment panoramic radiograph showed proper space closure and acceptable root parallelism, except for the mandibular left first premolar. There were no significant signs of bone or root resorption (Fig 7). Posttreatment lateral cephalometric analysis and superimposition showed no significant skeletal changes in the maxillary skeletal base (SNA, 82.1 ) and the mandibular skeletal base (SNB, 74.9 ). The maxillary anterior teeth were retracted and slightly tipped lingually. There was no significant improvement in the anteroposterior chin position since growth had already finished before treatment, so the patient still had a relatively convex profile (Fig 8; Table). To superimpose the multi-planar reconstruction images and for volume rendering, a new registration technique developed by Tai et al22,23
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Fig 7. Posttreatment panoramic radiograph and lateral cephalogram.
Fig 8. Cephalometric superimposition: black line, pretreatment; red line, posttreatment.
(Fig 9) was performed. At the 24-month follow-up, she had a stable occlusion, with the results of the orthodontic treatment maintained (Fig 10). DISCUSSION
A Class II malocclusion is difficult to treat. A stationary anchorage is 1 main factor that determines the success of the treatment. Stationary anchorage means that the anchorage unit does not move in reaction to the applied forces and moments.24 Conventional extraoral
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appliances are routinely used to establish maximum anchorage. However, many patients reject headgear wear because of social and esthetic concerns, and the success of this treatment solely depends on patient compliance.25 In many cases, lack of compliance results in the loss of anchorage and unsatisfactory treatment results. The growing demand for treatments requiring maximum curative effects with minimal cooperation has made temporary skeletal anchorage devices more promising as an excellent alternative to traditional orthodontic anchorage.
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Fig 9. Superimposing multiplanar reconstruction (MPR) images (A and B) and volume rendering (C-E) with 3D superimposition technique.
In patients with Class II Division 1 malocclusions, the chief complaint is usually an exaggerated horizontal overlap of the incisors. Patients and parents are routinely informed that, although there are no tooth size-arch length discrepancies, an anteroposterior skeletal discrepancy is present. Proffit26 stated that approximately 80% of white Class II patients have some mandibular deficiency, whereas only approximately 20% have excessive maxillary development. In the most severe Class II Division 1 malocclusions, orthognathic surgery to advance the mandible is often indicated. During the treatment of a patient with a high-angle Class II malocclusion, it is important to prevent extrusion of the mandibular posterior teeth with Class II forces. Another consideration in our patient was the correction of a deep overbite. To correct a deep overbite, for example, leveling a mandibular curve of Spee can be achieved by extrusion of posterior teeth.27 However, extrusion of the premolars and molars will result in increased lower facial height, steepening of the occlusal
plane, and downward and backward rotation of the mandible with a worsened Class II skeletal relationship.28,29 The long-term stability of such a correction is questionable. Intrusion of the maxillary anterior teeth to correct a deep overbite might be indicated in patients with a gummy smile.29 However, when the patient has an ideal smile arc, any maxillary incisor intrusion should be carefully monitored during treatment to prevent flattening of the smile arc.30 When smiling, our patient displayed 95% of her maxillary incisors but did not show any gingivae. Even though she did not have a gummy smile, to control the vertical dimension, a slight intrusion of the maxillary anterior teeth was indicated for her. Anterior bodily retraction is achieved by either directly applying a moment and force to an edgewise bracket or using lever-arm mechanics to change the point of force application closer to the center of resistance.31 In a lever-arm system, the desired tooth movement is obtained by adjusting the length of the lever arm and the point of
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Fig 10. Two-year posttreatment facial and intraoral photographs.
force application.31 In this system, a transpalatal arch is needed to control the point of force application in the posterior area.12 Instead of a transpalatal arch, temporary skeletal anchorage devices can be placed palatally to control the point of force application. The point of force application and the line of action of the force can be planned from the lateral cephalometric radiograph.32 Increasing the vertical forces in the anterior and posterior areas will reinforce anchorage, but increasing the intrusive force in the anterior segment makes torque control more complicated and flattens the occlusal plane.33 If vertical bowing of the lingual archwire occurs during space closure, the anterior and posterior vertical force differences should be checked. In this patient, instead of using high-pull headgear to reinforce the posterior anchorage unit during en-masse retraction of the maxillary anterior teeth, we used temporary skeletal anchorage devices. There are several advantages with lingual retractor (double J retractor) mechanics.34 This technique requires no complicated wire bending and can easily control retraction of the
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maxillary incisors. When compared with the conventional lingual segmental approach, no brackets need to be bonded to the anterior portion during the retraction period, so practitioners can easily apply this technique. CONCLUSIONS
The double J retractor is an esthetic, effective, and simplified option for closing spaces caused by tooth extractions. It uses a single point force, so by controlling the magnitude and direction of the force, it is easy to prevent unwanted tooth movements. Since it can easily retract the maxillary anterior dentition in the various vertical dimensions, it could be an effective alternative in appropriate situations for patients who are reluctant to use conventional fixed appliances. REFERENCES 1. Alexander RG. The Alexander discipline. Glendora, Calif: Ormco; 1986. p. 371-94. 2. Scuzzo G, Takemoto K. Invisible orthodontics. Berlin, Germany: Quintessence; 2003. p. 15-21.
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3. Lagravere MO, Flores-Mir C. The treatment effects of Invisalign orthodontic aligners: a systematic review. J Am Dent Assoc 2005; 136:1724-9. 4. Wong BH. Invisalign A to Z. Am J Orthod Dentofacial Orthop 2001; 121:540-1. 5. Womack WR, Ahn JH, Ammari Z, Castillo A. A new approach to correction of crowding. Am J Orthod Dentofacial Orthop 2002; 122:310-6. 6. Boyd RL, Miller RJ, Vlaskalic V. The Invisalign system in adult orthodontics: mild crowding and space closure cases. J Clin Orthod 2000;34:203-12. 7. Jang HJ, Roh WJ, Joo BH, Park KH, Kim SJ, Park YG. Locating the center of resistance of maxillary anterior teeth retracted by double J retractor with palatal miniscrews. Angle Orthod 2010; 80:1023-8. 8. Chen Y, Kyung HM, Zhao WT, Yu WJ. Critical factors for the success of orthodontic mini-implants: a systematic review. Am J Orthod Dentofacial Orthop 2009;135:284-91. 9. Park HS, Kwon DG, Sung JH. Nonextraction treatment with microscrew implant. Angle Orthod 2004;74:539-49. 10. Chung KR, Oh MY, Ko SJ. Corticotomy-assisted orthodontics. J Clin Orthod 2001;35:331-9. 11. Isaacson RJ, Lindauer SJ. Closing anterior openbites: the extrusion arch. Semin Orthod 2001;7:34-41. 12. Park YC, Choi KC, Lee JS, Kim TK. Lever-arm mechanics in lingual orthodontics. J Clin Orthod 2000;34:601-5. 13. Kucher G, Weiland FJ, Bantleon HP. Modified lingual lever arm technique. J Clin Orthod 1993;27:18-22. 14. Vanden Bulcke MM, Dermaut LR, Sachdeva RC, Burstone CJ. The center of resistance of anterior teeth during intrusion using the laser reflection technique and holographic interferometry. Am J Orthod Dentofacial Orthop 1986;90:211-20. 15. Kim SH, Park YG, Chung KR. Severe Class II anterior deep bite malocclusion treated with a C-lingual retractor. Angle Orthod 2004; 74:280-5. 16. Nikolai RJ. Forces and structural analyses of representative orthodontic mechanics. In: Nikolai RJ, editor. Bioengineering analysis of orthodontic mechanics. Philadelphia: Lea and Febiger; 1985. p. 372-436. 17. AlQabandi A, Sadowsky C, BeGole EA. A comparison of the effects of rectangular and round archwires in leveling the curve of Spee. Am J Orthod Dentofacial Orthop 1999;116:522-9. 18. AlQabandi A, Sadowsky C, Sellke T. A comparison of continuous archwires and utility archwires for leveling the curve of Spee. World J Orthod 2002;3:159-65.
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19. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. Am J Orthod 1988;93:423-8. 20. Kojima Y, Fukui H, Miyajima K. The effect of friction and flexural rigidity of the archwire on canine movement in sliding mechanics: a numerical simulation with a 3-dimensional finite element method. Am J Orthod Dentofacial Orthop 2006;130:275.e1-10. 21. Kojima Y, Mizuno Y, Fukui H. A numerical simulation of tooth movement produced by molar uprighting spring. Am J Orthod Dentofacial Orthop 2007;132:630-8. 22. Tai K, Hotokezaka H, Park JH, Tai H, Miyajima K, Choi M, et al. Preliminary cone-beam computed tomography study evaluating dental and skeletal changes after treatment with a mandibular Schwarz appliance. Am J Orthod Dentofacial Orthop 2010;138:262.e1-11. 23. Tai K, Park JH, Mishima K, Hotokezaka H. Using superimposition of 3-dimensional cone-beam computed tomography images with surface-based registration in growing patients. J Clin Pediatr Dent 2010;34:361-8. 24. Diedrich P. Different orthodontic anchorage systems: a critical examination. Fortschr Kieferorthop 1993;54:156-71. 25. Egolf RJ, Begole EA, Upshaw HS. Factors associated with orthodontic patient compliance with intraoral elastic and headgear wear. Am J Orthod Dentofacial Orthop 1990;97:336-48. 26. Proffit WR. Contemporary orthodontics. 3rd ed. St Louis: C. V. Mosby; 1996. p. 2-22. 27. Bernstein RL, Preston CB, Lampasso J. Leveling the curve of Spee with a continuous archwire technique—a long-term cephalometric analysis. Am J Orthod Dentofacial Orthop 2007;131:363-71. 28. Shroff B, Lindauer SJ, Burstone CJ, Leiss JB. Segmented approach to simultaneous intrusion and space closure: biomechanics of the three-piece base arch appliance. Am J Orthod Dentofacial Orthop 1995;107:136-43. 29. Burstone CR. Deep overbite correction by intrusion. Am J Orthod 1977;72:1-22. 30. Sarver DM. The importance of incisor positioning in the esthetic smile: the smile arc. Am J Orthod Dentofacial Orthop 2001;120:98-111. 31. Gjessing P. Controlled retraction of maxillary incisors. Am J Orthod Dentofacial Orthop 1992;101:120-31. 32. Keles A, Erverdi N, Sezen S. Bodily distalization of molars with absolute anchorage. Angle Orthod 2003;73:471-82. 33. Creekmore T. Lingual orthodontics—its renaissance. Am J Orthod 1989;96:120-37. 34. Kim SH, Park YG, Chung KR. Severe anterior open bite malocclusion with multiple odontoma treated by C-lingual retractor and horseshoe mechanics. Angle Orthod 2003;73:206-12.
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Esthetic orthodontic treatment with a double J retractor and temporary anchorage devices Jae Hyun Park,a Kiyoshi Tai,b Masato Takagi,c Kuniaki Miyajima,d Yukio Kojima,e and Bo-Hoon Joof Mesa, Ariz, Okayama and Nagoya, Japan, St Louis, Mo, and Seoul, Korea
This clinical article reports an esthetic treatment option for managing a Class II malocclusion in an adult. The patient, a woman aged 24 years 2 months, had crowding and a convex profile. She was treated with maxillary first premolar extractions, a double J retractor, and temporary skeletal anchorage devices in the maxillary arch. Posttreatment records after 2 years showed excellent results with good occlusion and long-term stability. (Am J Orthod Dentofacial Orthop 2012;141:796-805)
T
he correction of dental crowding is a common orthodontic treatment that can be performed with a removable or fixed appliance or a combination of both. Until recently, the process of straightening teeth has typically involved appliances including brackets, bands, and wires, but many adult patients are reluctant to wear fixed appliances. Consequently, the desire for a cosmetic solution for misaligned teeth has caused more patients to seek veneers, crowns, and other laboratory-fabricated cosmetic restorations. Clear brackets can be placed for esthetic reasons, but they can irritate soft tissues because of their size. Lingual brackets might be a great alternative for those who desire straight teeth without visible brackets, but, although lingual orthodontic techniques have improved, they generally require more chair time and might not be cost-effective.1,2 Clear removable appliances have the benefits of improved oral hygiene and esthetics.3-6
a Associate professor and chair, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, Mesa, Ariz; international scholar, Graduate School of Dentistry, Kyung Hee University, Seoul, Korea. b Visiting adjunct assistant professor, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, Mesa, Ariz; private practice, Okayama, Japan. c Private practice, Okayama, Japan. d Adjunct professor, Center for Advanced Dental Education, Saint Louis University, St Louis, Mo. e Associate professor, Department of Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan. f Adjunct professor, Department of Orthodontics, Samsung Medical Center, College of Medicine, Sungkyunkwan University, Seoul, Korea; private practice, Seoul, Korea. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Jae Hyun Park, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A. T. Still University, 5835 E Still Cir, Mesa, AZ 85206; e-mail, [email protected]. Submitted, August 2010; revised and accepted, January 2011. 0889-5406/$36.00 Copyright Ó 2012 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2011.01.024
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These appliances have become increasingly popular among adults who want to straighten their teeth without using conventional brackets. However, in orthodontics, precisely controlled force application is required to achieve the final alignment. The purpose of this article is to report the use of a modified type of lingual retractor, the double J retractor, and temporary skeletal anchorage devices for enmasse retraction of the 6 anterior teeth in a patient with premolar extractions.7
DIAGNOSIS AND ETIOLOGY
A woman aged 24 years 2 months was referred by a general dentist for evaluation of anterior crowding. Her chief complaint was the appearance of her maxillary anterior teeth and upper lip (Fig 1). She did not want to have fixed orthodontic appliances in the maxillary arch because of their appearance, especially when smiling. She had a convex profile and a Class II skeletal pattern, with a Class II Division 1 malocclusion. Her facial form was mesocephalic, with good symmetry, a mildly increased lower facial height, and a retrognathic chin. Lip competence could be achieved but with some mentalis strain. There were no signs of temporomandibular joint dysfunction, and mandibular movements were normal, with no evidence of deviation. Intraorally, her maxillary and mandibular midlines were centered relative to her facial midline. All permanent teeth were present, and she had fair oral hygiene and probing depths within the norms. The patient was in good general health and had no history of major systemic diseases. She had no history of dental trauma or parafunctional habits, and the etiology of her occlusion was believed to be heredity. Pretreatment records showed that the patient had an end-on Class II relationship on the right and the left at the
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Fig 1. Pretreatment facial and intraoral photographs.
first molars and canines. There was moderate crowding in the maxillary arch and mild crowding in the mandibular arch with a severe curve of Spee. She had a 6.3-mm overjet and an 80% overbite. The teeth were free of caries with no pathologies. The third molars were missing. The cephalometric analysis indicated skeletal Class II (ANB, 8.4 ; Wits, 3.6 mm) with a hyperdivergent growth pattern (SN-MP, 44.9 ). The maxillary incisors were slightly retroclined (U1-SN, 96.2 ) caused by bilateral rotation of the maxillary central incisors, and the mandibular incisors showed a slight retroclincation (IMPA, 88.3 ) (Fig 2; Table). TREATMENT OBJECTIVES AND PLAN
The treatment objectives were to obtain normal overjet and overbite, establish Class I canine and molar relationships, relieve the crowding in both arches, level the
curve of Spee, and improve the patient's profile without the use of labial fixed appliances in the maxillary arch. With temporary skeletal anchorage devices, distal movement of the anterior or posterior teeth or both, without anchorage loss, would be possible.8,9 This patient wanted to retract her upper lip as much as possible, so the maxillary first premolars were extracted, but, to camouflage the skeletal Class II pattern, the mandibular second premolars were not extracted. TREATMENT ALTERNATIVES
With no growth modification possible, correction of the Class II molar relationship could be accomplished by nonextraction molar distalization treatment, extraction of the maxillary first premolars and the mandibular second premolars, or extraction of only the maxillary first premolars.
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Fig 2. Pretreatment panoramic radiograph and lateral cephalogram.
Table. Cephalometric measurements Measurement SNA ( ) SNB ( ) ANB ( ) Wits (mm) SN-MP ( ) FH-MP ( ) LFH (ANS-Me/N-Me) (%) U1-SN ( ) U1-NA ( ) IMPA ( ) L1-NB ( ) U1/L1 ( ) Upper lip (mm) Lower lip (mm)
Japanese norm 82.0 80.0 2.0 1.1 32.0 25.0 55.0 104.0 22.0 90.0 25.0 124.0 1.2 2.0
Pretreatment 83.5 75.0 8.4 3.6 44.9 35.0 57.1 96.2 12.8 88.3 28.2 130.6 4.1 4.8
To accomplish the treatment objectives, conventional esthetic treatment options for the maxillary orthodontic appliances included lingual orthodontic appliances or clear removable appliances. However, a difficult problem to overcome in lingual orthodontics has been torque control of the anterior teeth. A potential disadvantage of clear removable appliances is that they highly depend on patient compliance.6 The other significant weakness is the aligner cannot move the root apex efficiently which results in the tipping of teeth especially in extraction cases. Compared with those 2 esthetic orthodontic appliances, the double J retractor offered an effective tool for producing translational tooth movement during anterior retraction; a treatment plan was developed that included extraction of the maxillary first premolars, delivery of the double J retractor, and use of temporary skeletal anchorage devices to achieve bodily translation. Because of the skeletal discrepancies that resulted from an unfavorable growth pattern, bilateral sagittal
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Posttreatment 82.1 74.9 7.2 4.7 45.2 35.9 57.4 90.7 8.5 91.7 31.0 133.2 0.8 2.2
2 years posttreatment 79.9 75.1 4.8 2.7 45.0 35.3 57.3 94.7 14.8 88.3 28.7 131.7 0.6 2.0
split osteotomy was discussed for mandibular advancement combined with orthodontic treatment. Upon completion of the orthodontic treatment, genioplasty would be another option to improve her profile, but the patient declined all surgical options. TREATMENT PROGRESS
Before orthodontic treatment, the patient was referred to an oral surgeon to extract her maxillary first premolars. Because she had high esthetic demands and was unwilling to tolerate the extraction spaces, esthetic pontics were bonded to the distal aspects of the maxillary canines. The double J retractor is an alternative method for obtaining the desired direction of force on the maxillary anterior teeth.10-12 We used bonding pads instead of mesh brackets, which were common with earlier lingual retractors. The anterior lever arm hooks were bent in the wire approximately 20 mm from the pad so
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Fig 3. A, Schematic showing the double J retractor and palatal temporary anchorage devices: 1 and 2, palatal temporary skeletal anchorage devices; 3, anterior lever arm hooks; 4, posterior lever arm hooks. B, Maxillary occlusal photograph during treatment with a double J retractor and temporary skeletal anchorage devices. C, Maxillary occlusal photograph showing the bonded fixed appliance.
that the line of action of the force passed through the center of resistance. The posterior lever arm hooks were extended from the lingual crown surfaces of the canines. Both hooks can be used for space closing with elastic chains or superelastic closed-coil springs, and the posterior hooks can be used for torque control with Class II elastics. In this case, however, to minimize extrusion of the posterior mandibular teeth, the patient wore the Class II elastics at night only when it was necessary. After the retractor was adjusted to the lingual surface of the anterior teeth, it was bonded to them. Transbond (3M Unitek, Monrovia, Calif) was used, in addition to the customary bonding adhesive, to resist the shearing forces that occur when loading the retractor.13 Three temporary skeletal anchorage devices were placed (OSAS, Tuttlingen, Germany). Two (diameter, 1.6 mm; length, 8.0 mm) were placed palatally between the maxillary first and second molars, and 1 temporary anchorage device (diameter, 1.6 mm; length, 7.0 mm) was placed in the midpalate. Elastic chains or superelastic closed-coil springs were stretched from the anterior hooks to the temporary skeletal anchorage devices (Fig 3). A cephalometric film was used to determine the point of force application of the appliance with the aid of a gutta-percha cone as a radiopaque guide. Power elastic chains or nickel-titanium closed-coil springs that delivered 200 g per side provided the retraction force for space closure.14 In addition, the intrusion force of the lingual retractor was 60 g per side.15 Biomechanically, the position of the hook in the lever arm wire can change the point of force application with respect to the center of resistance of the teeth to be intruded and retracted. During lingual retraction, the maxillary left posterior temporary skeletal anchorage device failed, so another (diameter, 1.6 mm; length, 8.0 mm; OSAS) was installed between the maxillary left second premolar and first molar. After 6 months, the anterior teeth were retracted so that only 1 to 1.5 mm of space
remained between the canines and the second premolars. At this point, the patient was satisfied with the results, and she agreed to allow the fixed appliances be bonded for axial control and root movement. The 0.022 3 0.028-in edgewise ceramic brackets were bonded in both arches. After leveling, 0.018 3 0.025in stainless steel wires were placed for the remaining space closure in the maxillary arch. At this point, the patient wanted to retract her upper lip a bit more. Because of her request during the space closure, the maxillary anterior teeth were slightly tipped lingually (Fig 3). In the mandibular arch, during the leveling stage, a sectional 0.016-in copper-nickel-titanium wire was used between the mandibular incisors to achieve their initial leveling. Then a mandibular utility archwire was constructed with 0.016 3 0.022-in stainless steel wire. With a mandibular utility archwire, intrusive forces were applied to the mandibular incisors labially to the center of resistance. It produced a labial crown moment that resulted in proclination of the mandibular incisors.16 To minimize this side effect, labial root torque was included in the incisor region of the mandibular utility archwire.17,18 To produce approximately 60 g of incisor intrusion force, 20 of distal molar crown tip was activated.18 To prevent the need for mandibular molar extrusion, buccal root torque and expansion were applied to the molars by establishing cortical anchorage.18 After leveling the mandibular arch, a flat 0.016 3 0.022-in nickel-titanium archwire was used. At the finishing stage, a mild curve of Spee in the maxillary archwire and a mild reverse curve of Spee in the mandibular archwire were placed by using 0.018 3 0.025-in stainless steel wires. To establish acceptable overbite and overjet, intreproximal reduction was done on the mandibular anterior dentition during the finishing stage. A tooth positioner was used for final detailing. After treatment, the curve of Spee of the mandibular arch was found to be
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Fig 4. Three-dimensional finite element model for tooth-periodontal ligament system.
Fig 5. Retraction forces with A and B, temporary skeletal anchorage devices and C, elastics produce rotation of the anterior segment around the center of resistance.
successfully leveled. Active treatment time was 18 months. For a better esthetic result, an advancement genioplasty could have been considered. After treatment, maxillary and mandibular Essix retainers (Dentsply Raintree Essix, Sarasota, Fla) were delivered. The patient was instructed to wear them 24 hours per day for 1 year and then at night only. Recall visits for retainer checks occurred at 1, 3, and 6 months during the first year. To ensure continued satisfactory posttreatment alignment of the mandibular and maxillary anterior dentition, the use of retainers was recommended indefinitely.19 The detailed calculation method has already been described in previous articles.20,21 For our patient, the double J retractor was constructed of a segmented archwire bonded to the 6
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anterior teeth, and lever arms extended from the segmented archwire. Both were made of a stiff 0.028-in steel wire (Young's modulus, 200 GPa), and forces were applied at the ends of the lever arm. Assuming symmetry on both sides of the arch, a model of only the left side was fabricated. A lateral view of the finite element model is shown in Figure 4. By using this method, orthodontic tooth movement is calculated based on bone remodeling: ie, resorption and apposition of the alveolar bone. The boneremodeling rate is assumed to be in proportion to stress in the periodontal ligament. Jang et al7 reported that the center of resistance of the 6 maxillary anterior teeth is located vertically 12.2 mm (55.6%) and apically to the incisal edges of central incisors. Those authors also demonstrated that
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Fig 6. Posttreatment facial and intraoral photographs.
temporary skeletal anchorage devices located 8 mm apically to the cervical line of the first molars achieved bodily anterior retraction with a double J retractor. The center of resistance of the anterior teeth was determined from movement patterns when changing the location of the lever arm end. Figure 4 shows the movement patterns of the 6 anterior teeth and the stress distributions in the periodontal ligament after retraction of the teeth by 4 mm. When an extension line of the force passed through the center of resistance of the 6 anterior teeth, the teeth moved bodily and intruded by 0.5 mm. When an extension line of the force was coronal to the center of resistance, the anterior teeth tipped lingually. When an extension line of the force was apical to the center of resistance, there was lingual root movement (Fig 5). TREATMENT RESULTS
The posttreatment records demonstrate that the treatment objectives were achieved. The facial
photographs showed improved smile and profile esthetics (Fig 6). Class I canine and Class II molar relationships were established with a canine-protected occlusion. The dental midlines were maintained with the facial midline, and ideal overbite and overjet were achieved, and the curve of Spee was successfully leveled. The posttreatment panoramic radiograph showed proper space closure and acceptable root parallelism, except for the mandibular left first premolar. There were no significant signs of bone or root resorption (Fig 7). Posttreatment lateral cephalometric analysis and superimposition showed no significant skeletal changes in the maxillary skeletal base (SNA, 82.1 ) and the mandibular skeletal base (SNB, 74.9 ). The maxillary anterior teeth were retracted and slightly tipped lingually. There was no significant improvement in the anteroposterior chin position since growth had already finished before treatment, so the patient still had a relatively convex profile (Fig 8; Table). To superimpose the multi-planar reconstruction images and for volume rendering, a new registration technique developed by Tai et al22,23
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Fig 7. Posttreatment panoramic radiograph and lateral cephalogram.
Fig 8. Cephalometric superimposition: black line, pretreatment; red line, posttreatment.
(Fig 9) was performed. At the 24-month follow-up, she had a stable occlusion, with the results of the orthodontic treatment maintained (Fig 10). DISCUSSION
A Class II malocclusion is difficult to treat. A stationary anchorage is 1 main factor that determines the success of the treatment. Stationary anchorage means that the anchorage unit does not move in reaction to the applied forces and moments.24 Conventional extraoral
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appliances are routinely used to establish maximum anchorage. However, many patients reject headgear wear because of social and esthetic concerns, and the success of this treatment solely depends on patient compliance.25 In many cases, lack of compliance results in the loss of anchorage and unsatisfactory treatment results. The growing demand for treatments requiring maximum curative effects with minimal cooperation has made temporary skeletal anchorage devices more promising as an excellent alternative to traditional orthodontic anchorage.
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Fig 9. Superimposing multiplanar reconstruction (MPR) images (A and B) and volume rendering (C-E) with 3D superimposition technique.
In patients with Class II Division 1 malocclusions, the chief complaint is usually an exaggerated horizontal overlap of the incisors. Patients and parents are routinely informed that, although there are no tooth size-arch length discrepancies, an anteroposterior skeletal discrepancy is present. Proffit26 stated that approximately 80% of white Class II patients have some mandibular deficiency, whereas only approximately 20% have excessive maxillary development. In the most severe Class II Division 1 malocclusions, orthognathic surgery to advance the mandible is often indicated. During the treatment of a patient with a high-angle Class II malocclusion, it is important to prevent extrusion of the mandibular posterior teeth with Class II forces. Another consideration in our patient was the correction of a deep overbite. To correct a deep overbite, for example, leveling a mandibular curve of Spee can be achieved by extrusion of posterior teeth.27 However, extrusion of the premolars and molars will result in increased lower facial height, steepening of the occlusal
plane, and downward and backward rotation of the mandible with a worsened Class II skeletal relationship.28,29 The long-term stability of such a correction is questionable. Intrusion of the maxillary anterior teeth to correct a deep overbite might be indicated in patients with a gummy smile.29 However, when the patient has an ideal smile arc, any maxillary incisor intrusion should be carefully monitored during treatment to prevent flattening of the smile arc.30 When smiling, our patient displayed 95% of her maxillary incisors but did not show any gingivae. Even though she did not have a gummy smile, to control the vertical dimension, a slight intrusion of the maxillary anterior teeth was indicated for her. Anterior bodily retraction is achieved by either directly applying a moment and force to an edgewise bracket or using lever-arm mechanics to change the point of force application closer to the center of resistance.31 In a lever-arm system, the desired tooth movement is obtained by adjusting the length of the lever arm and the point of
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Fig 10. Two-year posttreatment facial and intraoral photographs.
force application.31 In this system, a transpalatal arch is needed to control the point of force application in the posterior area.12 Instead of a transpalatal arch, temporary skeletal anchorage devices can be placed palatally to control the point of force application. The point of force application and the line of action of the force can be planned from the lateral cephalometric radiograph.32 Increasing the vertical forces in the anterior and posterior areas will reinforce anchorage, but increasing the intrusive force in the anterior segment makes torque control more complicated and flattens the occlusal plane.33 If vertical bowing of the lingual archwire occurs during space closure, the anterior and posterior vertical force differences should be checked. In this patient, instead of using high-pull headgear to reinforce the posterior anchorage unit during en-masse retraction of the maxillary anterior teeth, we used temporary skeletal anchorage devices. There are several advantages with lingual retractor (double J retractor) mechanics.34 This technique requires no complicated wire bending and can easily control retraction of the
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maxillary incisors. When compared with the conventional lingual segmental approach, no brackets need to be bonded to the anterior portion during the retraction period, so practitioners can easily apply this technique. CONCLUSIONS
The double J retractor is an esthetic, effective, and simplified option for closing spaces caused by tooth extractions. It uses a single point force, so by controlling the magnitude and direction of the force, it is easy to prevent unwanted tooth movements. Since it can easily retract the maxillary anterior dentition in the various vertical dimensions, it could be an effective alternative in appropriate situations for patients who are reluctant to use conventional fixed appliances. REFERENCES 1. Alexander RG. The Alexander discipline. Glendora, Calif: Ormco; 1986. p. 371-94. 2. Scuzzo G, Takemoto K. Invisible orthodontics. Berlin, Germany: Quintessence; 2003. p. 15-21.
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3. Lagravere MO, Flores-Mir C. The treatment effects of Invisalign orthodontic aligners: a systematic review. J Am Dent Assoc 2005; 136:1724-9. 4. Wong BH. Invisalign A to Z. Am J Orthod Dentofacial Orthop 2001; 121:540-1. 5. Womack WR, Ahn JH, Ammari Z, Castillo A. A new approach to correction of crowding. Am J Orthod Dentofacial Orthop 2002; 122:310-6. 6. Boyd RL, Miller RJ, Vlaskalic V. The Invisalign system in adult orthodontics: mild crowding and space closure cases. J Clin Orthod 2000;34:203-12. 7. Jang HJ, Roh WJ, Joo BH, Park KH, Kim SJ, Park YG. Locating the center of resistance of maxillary anterior teeth retracted by double J retractor with palatal miniscrews. Angle Orthod 2010; 80:1023-8. 8. Chen Y, Kyung HM, Zhao WT, Yu WJ. Critical factors for the success of orthodontic mini-implants: a systematic review. Am J Orthod Dentofacial Orthop 2009;135:284-91. 9. Park HS, Kwon DG, Sung JH. Nonextraction treatment with microscrew implant. Angle Orthod 2004;74:539-49. 10. Chung KR, Oh MY, Ko SJ. Corticotomy-assisted orthodontics. J Clin Orthod 2001;35:331-9. 11. Isaacson RJ, Lindauer SJ. Closing anterior openbites: the extrusion arch. Semin Orthod 2001;7:34-41. 12. Park YC, Choi KC, Lee JS, Kim TK. Lever-arm mechanics in lingual orthodontics. J Clin Orthod 2000;34:601-5. 13. Kucher G, Weiland FJ, Bantleon HP. Modified lingual lever arm technique. J Clin Orthod 1993;27:18-22. 14. Vanden Bulcke MM, Dermaut LR, Sachdeva RC, Burstone CJ. The center of resistance of anterior teeth during intrusion using the laser reflection technique and holographic interferometry. Am J Orthod Dentofacial Orthop 1986;90:211-20. 15. Kim SH, Park YG, Chung KR. Severe Class II anterior deep bite malocclusion treated with a C-lingual retractor. Angle Orthod 2004; 74:280-5. 16. Nikolai RJ. Forces and structural analyses of representative orthodontic mechanics. In: Nikolai RJ, editor. Bioengineering analysis of orthodontic mechanics. Philadelphia: Lea and Febiger; 1985. p. 372-436. 17. AlQabandi A, Sadowsky C, BeGole EA. A comparison of the effects of rectangular and round archwires in leveling the curve of Spee. Am J Orthod Dentofacial Orthop 1999;116:522-9. 18. AlQabandi A, Sadowsky C, Sellke T. A comparison of continuous archwires and utility archwires for leveling the curve of Spee. World J Orthod 2002;3:159-65.
805
19. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. Am J Orthod 1988;93:423-8. 20. Kojima Y, Fukui H, Miyajima K. The effect of friction and flexural rigidity of the archwire on canine movement in sliding mechanics: a numerical simulation with a 3-dimensional finite element method. Am J Orthod Dentofacial Orthop 2006;130:275.e1-10. 21. Kojima Y, Mizuno Y, Fukui H. A numerical simulation of tooth movement produced by molar uprighting spring. Am J Orthod Dentofacial Orthop 2007;132:630-8. 22. Tai K, Hotokezaka H, Park JH, Tai H, Miyajima K, Choi M, et al. Preliminary cone-beam computed tomography study evaluating dental and skeletal changes after treatment with a mandibular Schwarz appliance. Am J Orthod Dentofacial Orthop 2010;138:262.e1-11. 23. Tai K, Park JH, Mishima K, Hotokezaka H. Using superimposition of 3-dimensional cone-beam computed tomography images with surface-based registration in growing patients. J Clin Pediatr Dent 2010;34:361-8. 24. Diedrich P. Different orthodontic anchorage systems: a critical examination. Fortschr Kieferorthop 1993;54:156-71. 25. Egolf RJ, Begole EA, Upshaw HS. Factors associated with orthodontic patient compliance with intraoral elastic and headgear wear. Am J Orthod Dentofacial Orthop 1990;97:336-48. 26. Proffit WR. Contemporary orthodontics. 3rd ed. St Louis: C. V. Mosby; 1996. p. 2-22. 27. Bernstein RL, Preston CB, Lampasso J. Leveling the curve of Spee with a continuous archwire technique—a long-term cephalometric analysis. Am J Orthod Dentofacial Orthop 2007;131:363-71. 28. Shroff B, Lindauer SJ, Burstone CJ, Leiss JB. Segmented approach to simultaneous intrusion and space closure: biomechanics of the three-piece base arch appliance. Am J Orthod Dentofacial Orthop 1995;107:136-43. 29. Burstone CR. Deep overbite correction by intrusion. Am J Orthod 1977;72:1-22. 30. Sarver DM. The importance of incisor positioning in the esthetic smile: the smile arc. Am J Orthod Dentofacial Orthop 2001;120:98-111. 31. Gjessing P. Controlled retraction of maxillary incisors. Am J Orthod Dentofacial Orthop 1992;101:120-31. 32. Keles A, Erverdi N, Sezen S. Bodily distalization of molars with absolute anchorage. Angle Orthod 2003;73:471-82. 33. Creekmore T. Lingual orthodontics—its renaissance. Am J Orthod 1989;96:120-37. 34. Kim SH, Park YG, Chung KR. Severe anterior open bite malocclusion with multiple odontoma treated by C-lingual retractor and horseshoe mechanics. Angle Orthod 2003;73:206-12.
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